Amnesty International accuses Nigeria's biggest petroleum producer, Shell, of manipulating oil spill investigations and documents in cases where the rights group says the company has wrongly reported on the cause and volume of pollution devastating the Niger Delta and made false claims about cleanup measures.

The future of farmers and fishermen whose livelihoods are destroyed by such spills depends on reports that can be ?very subjective, misleading and downright false,? according to an independent US industry expert hired by Amnesty International to review documents newly obtained under Nigeria's freedom of information law.

The Amnesty report offers detailed analysis to back longstanding charges that oil companies blame sabotage for spills sometimes caused by corrosion and other faults in aging pipelines. Sabotage or oil theft means a community is not eligible for compensation.

?Solutions to the terrible tragedy of oil pollution in the Niger Delta need to be found,? said a statement provided in response to the report. Shell was the first company to start producing oil in the delta, in 1958.

Shell repeated assertions that most spills are caused by growing theft that experts estimate at between 100,000 and 200,000 barrels of oil a day.

One questionable report claiming sabotage was accepted by a Netherlands court that ruled against compensation for a Niger Delta community, Amnesty noted.

Its report, in collaboration with Nigeria's Centre for Environment, Human Rights and Development, sheds new light on one of the worst environmental disasters in Nigeria, a 2008 spill that affected about 30,000 people in the delta's Bodo creek area and is the subject of a lawsuit in Britain.

Some experts say the spill caused the largest loss of mangrove habitat ever caused by an oil spill.

Shell documents say the leak started Oct. 5 and 1,640 barrels of oil were spilled. Government and community documents say the leak started Aug. 28. US-based Accufacts, the industry expert hired by Amnesty, reviewed a video of the leak and estimated that up to 4,320 barrels of oil was flooding Bodo each day for at least 72 days.

When Amnesty challenged Shell with its evidence, the company for the first time said it had turned off supply to the affected pipe, and therefore the volume of the spill could not be that high. Yet the video shows oil spurting months later, on Nov. 7.

Shell says it cleaned up the Bodo spill between Oct. 30, 2008 and December 2009. But it also says it did not have access to the area to stop a second major spill that began on Dec. 7, 2008.

Nigerian regulators have not certified the site as clean, as mandated by law.

Martyn Day of Leigh Day, the British law firm representing about 15,000 people from Bodo, said Amnesty's report ?makes it now clear that Shell have a totally deficient system ... that has led to a massive underestimate of how much oil has leaked out into that area.? He called Shell's estimate of the Bodo spill ?total nonsense.? ?Many thousands of hectares of mangrove creek have been devastated,? he said. ?Bodo was a fishing community that was thriving and vibrant and it is now almost dead: people's livelihoods have gone, the community has gone, the spirit has gone. It is a very, very sad town.? Other reports, including by the U.N. Environmental Program in 2011, have questioned Shell data on cleanups and remediation.

In response to mounting criticism, Shell in 2011 began publishing on its website the spillage reports that are drawn up by a committee including community members. But the oil company remains very much in charge of the process, which presents a conflict of interest, Amnesty said.

For the first time, its report documented the extent of oil spills in the Niger Delta – at least 3,000 over the past six years by the three main companies producing oil onshore.

And it disclosed the first figures showing that the Nigerian Agip Oil Company, a subsidiary of the Italian company ENI, has suffered twice as many spills as Shell, though it operates over a much smaller area. ?In 2012, there were a staggering 474 spills from Agip's operations, compared with 207 from Shell,? the report said.

The Associated Press was unable to reach ENI or its Nigerian subsidiary for comment. A website offering jobs says ?AGIP recognizes that industry activities on Idu island will increase pressure on most aspects of community life. AGIP is implementing a community relations policy premised on stakeholding for sustainability.?

Amnesty International also charged that Nigeria's government, which has shares in both Shell Nigeria and AGIP, ?is failing in its duty to control the oil industry and prevent environmental damage and human rights abuses.?

The organization called for the government of Italy and the Netherlands-to convene a public review of their oil companies? operations in Nigeria to ensure better oversight and an effective remedy for people whose rights have been abused in the Niger Delta.